Scaling/Moving doesn't work properly
This is expected behavior with the mirror modifier.

You have the clipping checkbox selected on the modifier, which means that any vertices that are on the mirror plane get stuck to that plane, and can only move along it, not off of it. To disable this sticking behaviour, you can just uncheck the clipping box.

However, scaling /moving etc will still only move the actual vertices you are editing, not the virtual ones created by the modifier.